List of features to be implemented (not in any particular order)
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- lasso selection tool
- prefs file, save prefs
- flatten (incl undo/redo...) - enabled only if nlayers>1
- resize selection
- text tool, font chooser, default font
- color chooser (papercolor, pen color); maybe more default colors
- printing: print-options, save printer settings (throughout a session,
   and on disk) (maybe a separate config file .xournal/gnome-print-settings)
- help index
- pressure sensitivity
- insert images (screen capture or from file or from clipboard), 
  not as full-page backgrounds (new ITEM type)
- more pen/highlighter shapes (chisel)
- convert to/from Jarnal format; to/from MS Journal format???
- recalibration upon screen resize / compensation for miscalibration
- find a better behavior for vertical space tool across page boundaries ?
- key mappings (pgup/dn for full page, up/dn for scroll)